The present invention relates generally to a disposable device for holding a blood tube. More particularly, the present invention relates to a carrier tube which receives a blood tube and is capped to create a liquid-tight and aerosol-tight seal which isolates the contents of the blood tube from the outside environment. The carrier tube is adaptable for use with centrifuge-type blood count systems.
As part of a routine physical or diagnostic examination of a patient, it is common for a physician to order a complete blood count for the patient. The patient's blood sample may be collected in one of two ways. In the venous method, a syringe is used to collect a sample of the patient's blood in a test tube containing an anticoagulation agent. A portion of the sample is later transferred to a narrow glass sample tube such as a capillary tube. The open end of the sample tube is placed in the blood sample in the test tube, and a quantity of blood enters the sample tube by capillary action. The sample tube has two fill lines at locations about its circumference, and the volume of blood collected should reach a level in the sample tube between the two fill lines. In the capillary method, the syringe and test tube are not used, and the patient's blood is introduced directly into the sample tube from a small incision made in the skin. In either case, the sample tube is then placed in a centrifuge, such as the Model 424740 centrifuge manufactured by Becton Dickinson and Company.
In the centrifuge, the sample tube containing the blood sample is rotated at a desired speed (typically 8,000 to 12,000 rpm) for several minutes. The high speed centrifugation separates the components of the blood by density. Specifically, the blood sample is divided into a layer of red blood cells, a buffy coat region consisting of layers of granulocytes, mixed lymphocytes and monocytes, and platelets, and a plasma layer. The length of each layer can then be optically measured, either manually or automatically, to obtain a count for each blood component in the blood sample. This is possible because the inner diameter of the sample tube and the packing density of each blood component is known, and hence the volume occupied by each layer and the number of cells contained within it can be calculated based on the measured length of the layer. Exemplary measuring devices that can be used for this purpose include those described in U.S. Pat. Nos. 4,156,570 and 4,558,947, both to Stephen C. Wardlaw, and the QBC.RTM. "AUTOREAD" centrifuged hematology system manufactured by Becton Dickinson and Company.
Several techniques have been developed for increasing the accuracy with which the various layer thickness in the centrifuged blood sample can be determined. For example, because the buffy coat region is typically small in comparison to the red blood cell and plasma regions, it is desirable to expand the length of the buffy coat region so that more accurate measurements of the layers in that region can be made. As described in U.S. Pat. Nos. 4,027,660, 4,077,396, 4,082,085 and 4,567,754, all to Stephen C. Wardlaw, and in U.S. Pat. No. 4,823,624, to Rodolfo R. Rodriguez, this can be achieved by inserting a precision-molded plastic float into the blood sample in the sample tube prior to centrifugation. The float has approximately the same density as the cells in the buffy coat region, and thus becomes suspended in that region after centrifugation. Since the outer diameter of the float is only slightly less than the inner diameter of the sample tube (typically by about 80 .mu.m), the length of the buffy coat region will expand to make up for the significant reduction in the effective diameter of the tube that the buffy coat region can occupy due to the presence of the float. By this method, an expansion of the length of the buffy coat region by a factor between 4 and 20 can be obtained. The cell counts calculated for the components of the buffy coat region will take into account the expansion factor attributable to the float.
Another technique that is used to enhance the accuracy of the layer thickness measurements is the introduction of fluorescent dyes (in the form of dried coatings) into the sample tube. When the blood sample is added to the sample tube, these dyes dissolve into the sample and cause the various blood cell layers to fluoresce at different optical wavelengths when they are excited by a suitable light source. As a result, the boundaries between the layers can be discerned more easily when the layer thickness are measured following centrifugation.
Typically, the centrifugation step and the layer thickness measurement step are carried out at different times and in different devices. That is, the centrifugation operation is first carried out to completion in a centrifuge, and the sample tube is then removed from the centrifuge and placed in a separate reading device so that the blood cell layer thicknesses can be measured. More recently, however, a technique has been developed in which the layer thicknesses are calculated using a dynamic or predictive method while centrifugation is taking place. This is advantageous not only in reducing the total amount of time required for a complete blood count to be obtained, but also in allowing the entire procedure to be carried out in a single device. Apparatus and methods for implementing this technique are disclosed in the aforementioned copending U.S. patent applications of Stephen C. Wardlaw entitled "Assembly for Rapid Measurement of Cell Layers", Ser. No. 08/814,536 which has issued as U.S. Pat. No. 5,889,581 and "Method for Rapid Measurement of Cell Layers ", Ser. No. 08/814,535 which has issued as U.S. Pat. No. 5,888,184.
In order to allow the centrifugation and layer thickness steps to be carried out simultaneously, it is necessary to freeze the image of the sample tube as it is rotating at high speed on the centrifuge rotor. This can be accomplished by means of a xenon flash lamp assembly that produces, via a lens and a bandpass filter, an intense excitation pulse of blue light energy (at approximately 470 nanometers) once per revolution of the centrifuge rotor. The pulse of blue light excites the dyes in the expanded buffy coat area of the sample tube, causing the dyes to fluoresce with light of a known wave length. The emitted fluorescent light resulting from the excitation flash is focused by a high-resolution lens onto a linear CCD (Charge Coupled Device) array. The CCD array is located behind a bandpass filter which selects the specific wavelength of emitted light to be imaged onto the CCD array.
The xenon flash lamp assembly is one of two illumination sources that are focused onto the sample tube while the centrifuged rotor is in motion. The other source is an array of light-emitting diodes (LEDs) which transmits red light through the sample tube for detection by the CCD array through a second band pass filter. The purpose of the transmitted light is to initially locate the beginning and end of the plastic float (which indicates the location of the expanded buffy coat area), and the fill lines. Further details of the optical reading apparatus may be found in the aforementioned copending application of Michael R. Walters entitled "Inertial Tube Indexer", Ser. No. 09/032,931, and in the aforementioned copending application of Bradley S. Thomas et al., entitled "Blood Centrifugation Device with Movable Optical Reader", Ser. No. 09/033,368.
Several problems exist with using a standard sample tube in a centrifugation device of the type described above. In particular, because the tube is made of glass, it is possible for the tube to shatter either during handling or during centrifugation if the tube is not properly handled or loaded. If this occurs, the blood sample in the tube can come in contact with the person handling the tube, or can become airborne if the tube is being centrifuged. Therefore, any pathogen that may be present in the blood sample can be spread to people in the immediate area of the centrifuge device. Also, the shattered tube can result in injury due to sharp edges or flying glass.
Furthermore, in the centrifuging techniques described above, the sample tube is not sealed prior to centrifugation. Hence, infectious agents that may exist in the blood sample can possibly become airborne during centrifugation even if the tube does not break.
Although it is possible to coat the sample tube with a shatterproofing material, this drastically increases the cost of the sample tube while only slightly improving safety. Furthermore, this technique does not positively isolate the blood sample in the tube from the outside atmosphere. As a result, some of the blood sample can still escape during centrifugation.
Accordingly, a continuing need exists for a technique which will obviate the above problems associated with standard glass sample tubes without redesigning or changing the physical makeup of the tube.